Personally, for a ~1 week trip I would do the Tokyo area or Kyoto/Osaka/Nara/Kobe/etc area, but not both. Especially since you've said that you are planning future trips anyway.

As your trip is in January I would do 5n Tokyo and 2n in one of the ski resorts up in Nagano or Yamagata. If you're not the ski'ing type then maybe Hakone or Kawaguchiko, etc?

Alternately 5n Kyoto, 2n Osaka, Kobe, Nara, etc.

If you insist on touching both areas then it depends whether you want more of the cultural/traditional side of Japan, or more of the pop culture side.